Most secreted and membrane proteins are processed in the endoplasmic reticulum (ER). The influx of proteins into the ER is coordinated with the capacity of the ER by a stress response mechanism, called the unfolded protein response (UPR). The UPR consists of three branches to respond to accumulation of unfolded protein within the lumen of the ER: IRE1/ERN1, PERK/EIF2AK3, and ATF6 (Walter et al., Science 2011, 334(6059): 1081-6). Whereas both ATF6 and IRE1 mainly increase the capacity of the ER by increasing transcription of ER chaperones, lipid synthesis genes and components of the ER-associated degradation (ERAD) machinery, PERK reduces de novo protein synthesis by directly phosphorylating eukaryotic initiation factor 2 alpha (eIF2alpha), thereby inhibiting global protein initiation. The UPR functions to restore ER homeostasis, and thus serves as a cellular survival mechanism under most physiologic ER stress conditions. However, under severe and unresolvable ER stress, the UPR can promote apoptosis through induction of the pro-apoptotic factor, CHOP (C/EBP homologous protein; GADD153).
Aberrant activation of the unfolded protein response has been implicated in a wide variety of pathologies as recently reviewed by Wang et al. (J. Cell Biol 2012, 197(7):857-67). Inhibition of the PERK-branch of the unfolded protein response relieves PERK-mediated protein translation inhibition, and hence derepresses protein synthesis under ER stress. This may be therapeutically useful in diseases associated with activation of the UPR, such as cancer, in particular secretory cancer types, diabetes (e.g. type 1 diabetes), obesity, ocular diseases, stroke, myocardial infarction, cardiovascular disease, atherosclerosis, arrhythmias, viral infectious and inflammatory diseases, and neurodegenerative diseases (such as amyotrophic lateral sclerosis, prion-related diseases, Huntington's, Alzheimer's and Parkinson's disease), and the like. An application of UPR-mediated cell death, is the efficacy of proteasome inhibitors (such as bortezomib/Velcade®) in the treatment of multiple myeloma: these malignant plasma cells are characterized by a high secretory burden due to constitutive secretion of immunoglobulins, and are exquisitely sensitive to inhibition of proteaseome activity which overwhelms the ER with unfolded proteins, and leads to CHOP-mediated apoptosis (Meister et al., Canc Res 2007, 67(4):1783-92).
WO 95/15758 describes the preparation of (hetero)arylquinazolines which inhibit CSF-1R receptor tyrosine kinase;
WO 97/03069 discloses heterocyclyl-substituted quinazolines as protein tyrosine kinase inhibitors;
WO 2005/070891 describes a class of compounds useful in treating cancer and angiogenesis;
WO 2011/119663 is directed to substituted indoline derivatives which are inhibitors of PERK.
There is a strong need for novel compounds which inhibit PERK kinase activity, thereby opening new avenues for the treatment or prevention of cancer, in particular secretory cancer types, diabetes (e.g. type 1 diabetes), obesity, ocular diseases, stroke, myocardial infarction, cardiovascular disease, atherosclerosis, arrhythmias, viral infectious and inflammatory diseases, and neurodegenerative diseases (such as amyotrophic lateral sclerosis, prion-related diseases, Huntington's, Alzheimer's and Parkinson's disease), and the like. It is accordingly an object of the present invention to provide such compounds.
The present invention is concerned with a chemical series of potent and selective inhibitors of PERK. These compounds are kinase-selective, not only compared to more than 400 unrelated kinases but also compared to the closely related eIF2alpha kinase family members, GCN2 and PKR. These compounds inhibit phosphorylation of eIF2α at 10-20 nM (IC50) in HEK293 cells, incubated with the ER stressor tunicamycin. These PERK inhibitors are selectively anti-proliferative in an ER-stressed epithelial cancer model (A549 cells with tunicamycin) at nM concentrations, but to a lesser extent in the absence of ER stress, illustrating the selectivity of these molecules in a cellular model. Furthermore, in the absence of an exogenous ER stressor, these PERK inhibitors induced ER stress (eg, as evidenced by induction of the pro-apoptotic CHOP gene) selectively in multiple myeloma cell lines and certain B-cell lymphoma cell lines (e.g. diffuse large B-cell lymphoma, mantle cell lymphoma, follicular lymphoma) at low nM concentrations, confirming the intrinsic sensitivity of multiple myeloma and B-cell lymphoma models to ER stress. The magnitude of this induction by PERK inhibitors was comparable to well-established ER stressors, such as tunicamycin, and correlated closely with reduced proliferation in malignant B-cell lines. In the tests performed, it was found that the induction of ER stress was maximal at a dose corresponding to approximately 50-75% inhibition of PERK.